The production of methane gas from subterranean coalbeds has become a common practice in recent years. In this regard, coalbeds that contain absorbed hydrocarbon gases (i.e., primarily methane) can be produced by the way of well bores drilled and completed into the coalbed formations (i.e., coal seams). The majority of methane gas contained within coalbed formations is absorbed into micropore and macropore systems within the coal. The micropore system is contained within the coal matrix while the macropores represent cleats within the coalbed formation. These cleats are interspersed throughout the coal matrix forming a fracture system that accounts for a majority of the permeability through the coalbed formation. In order to extract methane gas from a subterranean coalbed, a well is drilled into the coalbed formation that allows the methane gas to permeate through the cleats and into the well bore. This may require de-watering of the well.
Typically, wells (i.e., water, in-situ, gas, etc.) are completed by inserting a casing (e.g., steel or PVC) into the well bore extending into the earth. This well bore casing may be secured within the well bore by packing a permeable material, such as gravel, between the casing and the well bore. In this instance, the casing may include perforations in the section of the well bore that passes through a permeable formation of interest (e.g., an aquifer or coalbed). The perforated casing allows a fluid of interest (e.g., water or gas) within the permeable formation to permeate into the well bore where it may be extracted. Alternatively, a subterranean section of the casing in the permeable formation may be removed to allow the fluid to enter the well.
The removal of a subterranean section of the casing, or the expansion of a well bore diameter beneath the bottom of a well casing, is commonly referred to as an “open-hole” well completion. In this regard, a well bore casing is placed within the well and cemented into place. After the cement has cured, an under-reaming tool is placed down the bore of the casing in order to cut out a desired section of the casing (e.g., the section of the casing within a permeable formation). Once the casing within the permeable formation is removed, fluid from that formation may permeate directly into the well bore. Alternatively, a section of the well beneath the bottom of the casing (e.g., in a permeable formation) may be expanded in diameter using such an under-reaming tool, which again allows a fluid to permeate directly into the well bore. For example, methane gas in a permeable coalbed may permeate through cleats that are in communication with the open-hole section of the well. One benefit of the open-hole completion is that the under-reaming tool is able to create a section within the well having an increased diameter thereby increasing the interface with the permeable formation. In the case of coalbed methane gas wells, this allows additional cleats within the coalbed to communicate with the well, which allows for increased gas production.
Disadvantages of open-hole completion include the deposition of debris in the well bore during the under-reaming process and the lack of structure within the resulting open-hole section of the well bore. In this regard, the sides of the open-hole section may slough depositing debris (sometimes referred to as fines) in the well. Over time, this debris may accumulate within the open-hole section of the well bore and may clog or otherwise blocked the cleats thereby interfering with the production of gas from the well. Accordingly, this reduces the well's productivity.
In order to maintain the production of methane gas wells, it may be necessary from time to time to clean the well bore. Heretofore, this has entailed flushing the well wherein a pipe is inserted to the bottom of the well that applies fluid pressure (e.g., air, water or drilling fluids) in order to carry the debris to the surface.